Researches on an environmentally-friendly chemical process have been lately prevalent and many reports relating to the researches on important esterification reaction that is valuable in use are presented.
The dehydration-condensation reaction of a carboxylic acid and an alcohol using an acid catalyst is known as the most general method for producing an ester compound and specifically includes, for example, (1) a method comprising adding concentrated sulfuric acid (acid catalyst) to a solution of a carboxylic acid and methanol in dichloroethane followed by heating and refluxing, then separating an organic layer by diluting with water, and neutralizing the obtained organic layer with a saturated aqueous solution of sodium hydrogencarbonate and then distilling off the solvent to obtain an ester (Non-patent Literature 1; Experimental Chemistry Course (Jikken Kagaku Kouza), 1. Carboxylic acid and its derivative, 1.2 Esters, page 44, Experimental example 1.30) and (2) a method comprising adding concentrated sulfuric acid (acid catalyst) to a mixture of benzoic acid and anhydrous ethanol followed by heating and refluxing, then distilling off the unreacted alcohol under atmospheric pressure, and adding water of an amount of 5 times, and then neutralizing with solid sodium carbonate, and then extracting the separated oily material with ether, and washing the obtained ether layer with water and distilling off the ether to obtain an ester (Non-patent Literature 1; Experimental example 1.31), etc.
However, in case these methods is used as producing industrially an ester compound, it has not been satisfactory from the standpoint of green chemistry because these methods have the problem that a large amount of water is used for an extraction treatment to an organic layer and neutralization treatment for removing an acid catalyst (for example, a saturated aqueous solution of sodium hydrogencarbonate, and sodium carbonate and water) resulting in a large amount of waste water.
Under these conditions, development of a method for producing industrially an ester compound taking economic efficiency and environment into consideration has been desired.
[Non-patent Literature 1] “New Experimental Chemistry Course 14 (Shin Jikken Kagaku Kouza) Synthesis and reaction of organic compound II” edited by Corporation: The Chemical Society of Japan, published by MARUZEN CO., LTD, Dec. 20, 1977, 1. Carboxylic acid and its derivative, 1.2 Esters, page 44, Experimental examples 1.30 and 1.31)